VITAL SIGNS; Patterns: Mothers' Weight Tied to Youths' Asthma

By ANAHAD O'CONNOR

Published: August 23, 2011

Women who are overweight or obese when they become pregnant may be more likely to have children who develop asthma as teenagers, new research shows.

The findings could point to yet another consequence of the rising rates of obesity worldwide. Scientists have already documented a number of complications that are more likely to arise in women who are obese before they become pregnant, among them a greater risk of stillbirths, preterm deliveries and gestational hypertension.

The prevalence of asthma has risen substantially across the globe since the 1970s. In the latest study, a team of researchers from England and Finland sought to explore whether the obesity trend may have played a role, focusing on a group of about 7,000 teenagers who were born in northern Finland.

As part of the study, published in The Journal of Epidemiology & Community Health, the researchers questioned the mothers of the children about their lifestyles and backgrounds. They also collected detailed health histories of both parents, including medical records dating back to the time before the mothers became pregnant.

After controlling for a number of potentially complicating factors -- like a history of parental smoking or asthma -- the researchers found that the teenagers whose mothers had been overweight or obese just before they became pregnant were 20 to 30 percent more likely to have asthma or a history of wheezing. And the teenagers whose mothers were heaviest at the time of pregnancy were nearly 50 percent more likely to have had a history of severe wheezing.

But why would a mother's weight have any effect on a child's breathing later in life?

The researchers made it clear that their findings, while intriguing, did not show a causal link, only a strong correlation. Still, they pointed to previous research indicating that being overweight during pregnancy can throw a woman's metabolic, hormonal and ovarian activity into turmoil, which in turn can disrupt the normal development of a fetus. A higher body mass index during pregnancy can also set off a spike in levels of leptin, a hormone that binds to receptors in the fetal lung and may be critical to lung development in the womb.

Worldwide, up to 37 percent of teenagers show some symptoms of asthma. The researchers argued that if a mother's weight before pregnancy plays a role, then stepping up public health efforts to reduce obesity in pregnancy may, over time, help bring down the number of new asthma cases.

This is a more complete version of the story than the one that appeared in print.